CREATE TABLE orders ( order_id integer PRIMARY KEY, product_no integer REFERENCES products, quantity integer ); # 定义多个 Column 组成的外键,要求被约束列(外键)的数量和类型应该匹配被引用列(主键)的数量和类型。 CREATE TABLE t1 ( a integer PRIMARY KEY, b integer, c integer, FOREIGN KEY (b, ...
Summary: in this tutorial, you will learn about the PostgreSQL foreign key and how to add foreign keys to tables using foreign key constraints. Introduction to PostgreSQL Foreign Key Constraint In PostgreSQL, a foreign key is a column or a group of columns in a table that uniquely identifies ...
[ { UNION | INTERSECT | EXCEPT } [ ALL | DISTINCT ] select ] [ ORDER BY expression [ ASC | DESC | USING operator ] [ NULLS { FIRST | LAST } ] [, ...] ] [ LIMIT { count | ALL } ] [ OFFSET start [ ROW | ROWS ] ] [ FETCH { FIRST | NEXT } [ count ] { ROW | RO...
SET CONSTRAINTS设置当前事务的约束检查模式。SET CONSTRAINTS { ALL | name [, ...] } { DEFERRED | IMMEDIATE }SET SESSION AUTHORIZATION为当前会话设置会话用户标识符和当前用户标识符。SET [ SESSION | LOCAL ] SESSION AUTHORIZATION username SET [ SESSION | LOCAL ] SESSION AUTHORIZATION DEFAULT RESET ...
index_parameters in UNIQUE, PRIMARY KEY, and EXCLUDE constraints are: [ INCLUDE ( column_name [, ... ] ) ] [ WITH ( storage_parameter [= value] [, ... ] ) ] [ USING INDEX TABLESPACE tablespace_name ] exclude_element in an EXCLUDE constraint is: ...
Unique Constraints: ensure that the data contained in a column, or a group of columns, is unique among all the rows in the table. Primary Keys Constraint: both unique and not null. A table can only hasONEprimary key, although this primary key can be a group of columns (a composition ...
Partitioned tables do not support UNIQUE, PRIMARY KEY, EXCLUDE,orFOREIGN KEY constraints; however, you can define these constraints on individual partitions. When using range partitioning, a NOT NULL constraint isaddedto each non-expression column in the partition key. ...
select select_list from table1 where expr operator ( select select_list2 from table2) 总结: 子查询(内查询)在主查询之前一次执行完成; 子查询的结果被主查询(外查询)使用。 注意事项: 子查询要包含在括号内。 将子查询放在比较条件的右侧。
ccu.column_nameASforeign_column_nameFROMinformation_schema.table_constraintsAStcJOINinformation_schema.key_column_usageASkcuONtc.constraint_name = kcu.constraint_nameANDtc.table_schema = kcu.table_schemaJOINinformation_schema.constraint_column_usageASccuONccu.constraint_name = tc.constr...
List of fixed system views are sys.check_constraints, sys.data_spaces, sys.default_constraints, sys.dm_exec_connections, sys.foreign_keys, sys.key_constraints, sys.stats, sys.syscolumns, sys.sysforeignkeys, sys.sysprocesses, sys.system_objects, sys.table_types, sys.tables, sys.types, sys....